Dallas’ plan for levee fixes released for environmental review

The potential environmental effects of restoring Trinity River’s levees to 100-year flood protection are minor — and are far outweighed by the need to fix them, according to an environmental assessment released Monday.

That conclusion comes as little surprise. But the report, required by federal regulations to allow the public to voice environmental concerns, provides the most detailed view yet of exactly how Dallas officials plan to upgrade the levees.

And significantly, the report reveals a new hands-off approach by U.S. Army Corps of Engineers officials, who decline to endorse the city’s plan or weigh in on whether it will provide basic protection from a flooding Trinity River that could inundate some neighborhoods and signature properties such as the Hilton Anatole, the World Trade Center, the Infomart and American Airlines Center.

The corps “provides no opinion as to the efficacy of the modifications to provide flood risk management benefits,” the report says. It puts sole responsibility for that on City Hall’s engineering consulting firm, HNTB, which the report says is “responsible and liable for the adequacy and safety of a design.”

City Manager Mary Suhm and Assistant City Manager Jill Jordan did not respond to requests for comment on the report Monday.

The report’s new disclaimer by the Corps of Engineers marks a significant shift from an earlier draft of the report that the city submitted to the corps in June. A document obtained by Dallas Observer columnist Jim Schutze suggests the corps’ disclaimer may have come as a result of disagreements between corps and city officials.

The document, an internal corps memo prepared in June, mentions inserting the disclaimer and a line saying the corps endorses the city’s levee improvement plan only insofar as saying it won’t hurt the existing levees.

“Do we want to insert the disclaimer and start the process of informing higher HQ that we do not endorse what they are proposing?” the corps document says. “Or at least mention that we had some serious disagreements and therefore had to craft language to insert.”

After Hurricane Katrina flooded New Orleans in 2005, many critics blamed the corps, which responded by implementing more rigorous criteria for inspecting levees. Dallas’ levees, which were built in the 1930s and later overhauled, were among the first to be measured by those standards after Katrina.

Since 2009, when the corps released a critical inspection report on the Dallas levees, city officials have been racing to restore them. The report rated the levees “unacceptable.”

With the inspection report, corps officials also withdrew a 2006 letter of support they had sent to an engineering firm hired by the city, vouching for the levees’ ability to protect neighborhoods and businesses near them from a 100-year flood — a flood with a 1-in-100 chance of happening during any given year.

The withdrawal of that letter caused the Federal Emergency Management Agency to begin redrawing flood maps within the downtown Dallas flood plain. The newly drawn maps, not expected before 2014, could put thousands of property owners into a redefined flood plain and compel them to buy expensive insurance.

A major component of the city’s plan to restore the levees to FEMA’s 100-year flood standard involves building “cutoff walls” underground that run about 3.5 miles near the riverside edge of the levees. The walls are designed to keep water from seeping through sand underneath the levees, which could undermine them when the river rises.

This summer, after city officials turned in a draft of the plan, city and corps officials disagreed on what material should be used for these walls. City officials and their consultants called for a mixture of soil and a clay-like substance called bentonite. Corps officials argued for a much more expensive mixture of cement and bentonite.

By October, the corps had dropped its opposition to the cheaper material. This and other changes have brought the project’s estimated cost down from more than $100 million to perhaps less than $30 million.

City officials say a soil and bentonite mixture is standard for such walls. The corps perceived a risk that, if soil-bentonite was used, trenches built to house the walls could cave in on themselves during construction, damaging the levees.

When the corps reversed course, both city and corps officials said it was because the city will change the building process to make that risk negligible.

But that’s also when corps officials began to make clear that their only function in reviewing the city’s proposed restorations to 100-year flood protection is to ensure that those changes don’t harm the levees or interfere with long-range plans to restore them to 800-year flood protection.

In the 2009 inspection report, corps officials had said they would later determine whether to issue another letter of support vouching for the levee’s ability to meet FEMA’s 100-year standard. But corps officials said Monday that such a letter is no longer a possibility.

“Due to the FEMA remapping schedule, the city elected to work with the engineering firm of HNTB on the detailed investigations to identify the remediation measures required for the 100-year event,” corps spokesman Jim Frisinger said in an email. “It is now more appropriate that HNTB be responsible for certifying the levees once the remediation measures are completed.”

In the environmental assessment released Monday, passages suggesting the corps endorsed the city’s plan had been removed. Also removed was a line in the June draft statement that said the city’s levee improvements “are intended to be compatible” with future plans to restore the levees to the 800-year flood standard.

Local corps officials said Monday they could not immediately get authorization to comment on the deletion or whether they still consider the city’s 100-year fixes to be compatible with the corps’ longer-term plans to bring the levees up to the 800-year standard.

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